The Earth Shelter

One of the most innovative and ambitious examples of green construction on The Farm in recent years is an “earth shelter.” It was built to house an office space for one of the community’s members, and is currently serving as a space for women coming to The Farm to deliver their baby.

The back and sides of the structure are submerged into the side of a hill, using the thermal mass of the earth to insulate and regulate temperatures inside the building.

These three walls are built from cinder blocks filled with concrete and rebar (more mass) that have been properly treated to eliminate moisture from passing through to the inside.

earth shelter

The south face of the building is made primarily of glass. Light entering the building in winter months strikes the cement slab and slate floor along with block exterior and interior walls warming the thermal mass represented by the entire structure.

In addition, a split design in the roof provides a row of small windows (also facing south) to help bring in ambient light.

earth shelter

The end result: Very little external heating or cooling is necessary to maintain an even temperature inside the building.

Even without added heat, the temperature inside changes very little over night in winter months.

On the coldest days when skies are overcast and there is no sunshine, a small wood stove adds supplemental heat which again is absorbed by the building’s thermal mass.


However in summer months, heat absorbed and reflected off the cement patio across the south front causes the building to take on too much heat.

To combat this, a pergola has been built across the front to support a vine which in summer months provides shade. Air conditioning supplements the cooling in order to make work conditions more comfortable.

In order to serve as a more complete model of alternative construction and technology,the original owner installed a 4.2 KW solar photo voltaic system to supply virtually all of the building’s electrical needs. He has since moved these to another home outside The Farm.

State and Federal incentives and rebates supplied of up to three quarters of the total investment for the installation of solar panels and other hardware.

solar panels
The electricity generated by the panels did not charge batteries but were connected to or interfaced with the main electrical lines, otherwise known as a “grid-tie” system. (note: There are other several other grid- tie systems currently installed in the community.)An inverter converted the DC electricity from the panels into the AC voltage compatible with the grid.
The building had two meters, one that showed the amount of electricity that had been used and a second which showed the amount which had been generated.A monitoring system also calculated the total amount of generated power and other statistics. sloar grid tie
During winter months when daylight hours are short and there is often little sun for days at a time, the cost for electricity powering the building’s lights and equipment ran on average from $10 to $15 a month, still a substantial reduction from his pre-array electric bill.As the days increase in length even when powering supplemental air conditioning the panels generated more power than was consumed, with the excess feeding directly into the grid, in essence producing a financial credit. golf cart charging
The amount of financial incentive is enhanced because, at the time of this writing, TVA (the source of electricity from the grid) actually pays quite a bit more for the electricity that is produced than it charges for the power that is consumed.
Going one step further as a model of sustainability, a solar water heating system was installed to supply a small kitchen and bathroom. A radiator style collector heats a fluid similar to antifreeze which transfers the heat though indirect contact to water which is then stored in a large tank on the roof.The solar water heater worked well, but the amount of that water needed or used in the building is relatively small, and dollar for dollar, additional solar electric panels would have been a better investment. solar water heater

Reflecting on what might have been done differently to improve the energy efficiency or “green” aspects of the building, one option would have been to choose a different color for the roof. The roof is sheathed with a dark brown enamel coated tin which has a 40 year warranty and never needs painting. The color green was chosen to allow the building to better blend in with the environment, important since the structure is located only a short distance below the owner’s home. However a white or lighter color would have reflected rather than absorbed heat and could have helped keep the building cooler during Tennessee’s long, hot summers.

gardenThere’s one other aspect of sustainability around this site that is worth mentioning. Directly adjacent to the office is a fenced in garden. Periodically throughout the day, as a break from working at computers, time can be spent in the garden, planting, weeding, and harvesting, all following the permaculture model that sees home, work and food production as an integrated system.  All in all it is a powerful example of the sustainable lifestyle.

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